Process for the halogen modification of aluminophosphate molecular sieves and a product so produced

ABSTRACT

A process for treating crystalline aluminophosphates to provide aluminophosphates having modified catalytic properties. The crystalline aluminophosphates are contacted with a halogen-derived compound at an effective temperature and for an effective time to alter the surface characteristics of the aluminophosphates with resulting modification of catalytic properties.

BRIEF SUMMARY OF THE INVENTION

1. Technical Field

This invention is directed in general to a process for the treatment ofcrystalline aluminophosphate molecular sieves to provide adsorptive andmodified catalytic properties. This invention is directed toaluminophosphate molecular sieves which have been treated with fluorine,chlorine, bromine, iodine, interhalogen compounds, boron trifluoride,phosphorus trifluoride, phosphorus pentafluoride and mixtures thereofwhereby the changes in surface characteristics of the aluminophosphateresult in changes in the adsorptive properties and/or catalyticproperties.

2. Background Art

Although there are a few notable exceptions, the vast majority ofnaturally-occurring and synthetic crystalline molecular sieves containmost if not all of the framework atoms as AlO₄ -tetrahedra, i.e.,framework aluminum atoms, together with the SiO₄ -tetrahedra, comprisethe zeolite crystal framework. Relatively few molecular sieves have beenextensively studied which do not contain aluminum and silicon as theessential framework constituents.

Although it is generally accepted that the aluminum-containingstructural units in an aluminosilicate provide the so-called"acid-sites" which account for the catalytic activity of zeolites insuch hydrocarbon conversion reactions as catalytic cracking, the varioussites in aluminophosphates are not to be similarly viewed owing to thedifferent framework constituents. Since it is believed that the cationsites are responsible in one or more ways for the adsorptive preferenceof most zeolites for strongly polar molecules such as water, i.e. theirhydrophilic character, one can only speculate the effect of varioustreatment processes on different molecular sieves when such molecularsieves are vastly different in terms of their acid sites as a result ofdifferent framework structures.

A number of different techniques have heretofore been proposed to removeframework aluminum atoms from aluminosilicates to createaluminum-deficient lattice structures having fewer cation sites, andconsequently less hydrophilicity and more hydrophobicity, and alteredcatalytic activities. One of the more common early techniques fordealuminizing zeolites involves contacting either the hydrogen or thedecationized form of the zeolite with a known chelating agent foraluminum, such as ethylenediamine tetracetic acid (EDTA) oracetylacetone, and removing aluminum as an organometallic complex. Amore recent and more widely used procedure involves prolonged contact ofnon-metallic cation forms of zeolites with steam at elevatedtemperatures which can exceed 800° C. The most relevant processes fortreatment of aluminosilicates are discussed hereinafter.

U.S. Pat. No. 4,297,335 describes crystalline aluminosilicate zeolitecompositions which have been treated with a fluorine gas mixture toalter the framework aluminum content and cation sites and therebyenhance the hydrophobic character of the zeolites. The fluorine gasmixture is comprised of (i) from 0.1 to 20 volume percent fluorine, (ii)from zero to 21 volume percent oxygen and (iii) as the remainder, one ora mixture of two or more inert gases, preferably nitrogen. The startingcrystalline aluminosilicate zeolite compositions have at least 50percent of the framework aluminum atoms not associated with metalcations and are contacted with the fluorine gas mixture at a temperatureof from about 50° F. to 400° F.

Copending U.S. patent application Ser. No. 363,560, filed Mar. 30, 1982,now abandoned and commonly assigned, describes a process for enhancingthe hydrophobicity of crystalline aluminosilicate zeolites having aninitial SiO₂ /Al₂ O₃ molar ratio of at least 5. The zeolites are treatedwith pure chlorine gas at a temperature of from about 200° C. to about1000° C. and thereafter purged with a purge gas, i.e., nitrogen, toremove entrapped chlorine gas from the treated zeolite. This treatmentresults in modification of both the adsorptive properties, i.e.,enhanced hydrophobicity, and the catalytic properties of the zeolites.

H. K. Beyer and I. Belenykaja, A New Method for the Dealumination ofFaujasite-Type Zeolites, Catalysis be Zeolites, Printed in theNetherlands, 203-209 (1980) describes the dealumination offaujasite-type zeolites, particularly Y zeolites, using silicontetrachloride as the dealuminizing agent. This dealumination process iscarried out at high temperatures ranging from about 457° C. to about557° C.

French Pat. No. 2,303,764 describes a process for increasing the molarratio of SiO₂ /Al₂ O₃ in the crystalline skeleton of zeolites havingSiO₂ /Al₂ O₃ molar ratios of less than 5. The zeolites are firstdehydrated by heating to a temperature of at least 400° C. in a reactorequipped with at least one opening in the presence of air or inertgases. Thereafter, gases containing chlorine and/or hydrochloric acidare reacted with the dehydrated zeolite at temperatures between 400° C.and 700° C. It is stated that the zeolite product can then be treated bywashing with aqueous solutions of ammonium salts or salts which giveammonium ions, strong aqueous mineral acids, caustic soda or alkalinesolutions, or distilled water. Example 11 illustrates that the capacityof adsorption of zeolites with respect to water vapor is practically notaltered by treatment of the zeolites according to the process describedtherein.

In copending U.S. Ser. No. 403,928, filed Aug. 2, 1982, now abandonedbut followed by divisional application Ser. No. 725,503, filed Apr. 24,1985, now U.S. Pat. No. 4,569,833, commonly assigned, is a process whichinvolves the treatment of aluminosilicates and aluminophosphates withsilicon tetrafluoride. The process involves silicon substitution orrearrangement of the framework tetrahedral atoms.

None of the aforementioned items disclose a process for treatingcrystalline aluminophosphates according to the present invention inwhich the crystalline aluminophosphates are treated with a gas mixturecontaining: (i) from 0.1 to 100 volume percent of a halogen-derived gascomprising at least one of fluorine, chlorine, bromine, iodine,interhalogen compounds, boron trifluoride, phosphorus trifluoride andphosphorus pentafluoride; (ii) from zero to 21 volume percent oxygen;and (iii) optionally, as the remainder, one or a mixture of two or moreinert gases.

SUMMARY OF THE INVENTION

The present invention provides a process for treating aluminophosphates.The process generally comprises contacting a crystallinealuminophosphate with a gas comprising:

(i) from 0.1 to 100 volume percent of a halogen-derived gas comprisingat least one of fluorine, chlorine, bromine, iodine, interhalogencompounds, boron trifluoride, phosphorus trifluoride and phosphoruspentafluoride;

(ii) from zero to 21 volume percent oxygen gas; and

(iii) optionally, as the remainder, one or a mixture of two or moreinert gases, preferably nitrogen.

A preferred embodiment of the present invention comprises contacting thealuminophosphate obtained from the treatment with the halogen-derivedgas with an aqueous solution of salt, such as an ammonium salt solution,for a sufficient time to remove fluoride species, such as AlF⁺⁺ and AlF₂⁺, from the treated crystalline aluminophosphate. In addition the finalcrystalline aluminophosphate can be treated after the instant process bycalcination at temperatures from 100° C. up to the crystal destructiontemperature of the crystalline aluminophosphate and by rehydration or bya combination of ion exchange, calcination and rehydration treatments inany order.

DETAILED DESCRIPTION OF THE INVENTION

The crystalline aluminophosphates employed in the instant inventioninclude, among others, those described in U.S. Pat. No. 4,310,440 and,in particular, to the species denominated therein as AlPO₄ -5, AlPO₄ -8,AlPO₄ -9, AlPO₄ -11, AlPO₄ -12, AlPO₄ -14, AlPO₄ -16, AlPO₄ -17, AlPO₄-18, AlPO₄ -20, AlPO₄ -22, AlPO₄ -25, AlPO₄ -26, AlPO₄ -28, and AlPO₄-31. Reference to one of the aforementioned species is meant herein todenominate that species as described in U.S. Pat. No. 4,310,440. Inaddition the crystalline aluminophosphate, denominated AlPO₄ -33,disclosed in copending U.S. Ser. No. 480,698, filed Mar. 31, 1983, nowU.S. Pat. No. 4,473,663, issued Sept. 25, 1984 and incorporated hereinby reference thereto, may be employed herein. The crystallinealuminophophates of U.S. Pat. No. 4,310,440 are generally described ashaving a framework structure whose chemical composition expressed interms of mole ratios of oxides is: Al₂ O₃ : 1.0±0.2 P₂ O₅ ; each of saidframework structures being microporous in which the pores are uniformand have nominal diameters within the range of about 3 to about 10Angstroms, an intracrystalline adsorption capacity for water at 4.6 torrand 24° C. of at least 3.5 weight percent, the adsorption and desorptionof water being completely reversible while retaining the same essentialframework topology in both the hydrated and dehydrated state.

The terms "halogen-derived gas" and "halogen-derived compounds" areemployed herein to include at least one of the group consisting offluorine, chlorine, bromine, iodine, interhalogen compounds, borontrifluoride, phosphorus trifluoride and phosphorus pentafluoride. Theterm "interhalogen compounds" denominates compounds formed from two ormore halogens, e.g., ClF₃ and BrF₅.

The crystalline aluminophosphates may be calcined at above about 100° C.for a period of about 0.1 hours or more prior to being contacted with ahalogen-derived gas mixture comprising: (1) from 0.1 to 100 volumepercent of a halogen-derived gas, preferably from about 0.25 to about 50volume percent and more preferably from about 1 to about 25 volumepercent of a halogen-derived gas; (2) from zero to 21 volume percentoxygen and (3) optionally, as the remainder, one or a mixture of two ormore inert gases. The inert gas is preferably present in an amount fromabout 50 to about 99.75 volume percent and is preferably one or amixture of two or more inert gases such as nitrogen, helium, argon andthe like. When oxygen and nitrogen are present in the gas mixture, theuse of dry air is particularly beneficial. The inert gas acts as adiluent to adjust the halogen-derived gas concentration to a desiredlevel. Low concentrations of the halogen-derived gas in the gas mixtureare desirably and effectively used in the process of this invention.However, the gas mixture can contain higher concentrations up to 100volume percent of the halogen-derived gas.

The crystalline aluminophosphates are contacted with halogen-derived gasat an effective temperature and is preferably from about 20° C. to about200° C. for an effective period of time to affect the surfacecharacteristics of the aluminophosphate. The more preferred temperaturefor contacting the halogen-derived gas with the crystallinealuminophosphate is from about 20° C. to about 100° C. and mostpreferably is at about room temperature (18° C. to 22° C.). The processof this invention is preferably carried out at ambient pressure (14.7psia), however both atmospheric and superatmospheric pressure conditionsmay be employed in this process. In general, the effective contact timecan vary from a few minutes or less to several hours or longer, i.e.,from 1 minute or shorter to 10 hours or longer. The preferred contacttime is from about 10 minutes to about four hours. It is readilyappreciated that the required contact time will be influenced by thereaction temperature, total pressure, concentration and flow rate of thehalogen-derived gas mixture, concentration and choice of the crystallinealuminophosphate and other factors. The process of the present inventionis suitably conducted under operative conditions which give reasonablereaction rates and, of course, the desired modification of thecrystalline aluminophosphates.

After the crystalline aluminophosphates are contacted withhalogen-derived gas under the above described operational conditions,the aluminophosphates are preferably treated with an aqueous solution ofat least one salt for a sufficient period of time to remove at leastsome of any fluoride species associated with the treated crystallinealuminophosphate. Aqueous salt solutions of ammonium or aluminium aregenerally employable. The removal of the fluoride species can preventthe corrosion of equipment utilized in carrying out the process of thepresent invention and also equipment used in processes employing thehalogen treated aluminophosphates such as catalytic cracking reactions.The crystalline aluminophosphates are preferably contacted one or moretimes, most preferably three times, with an aqueous solution of ammoniumor metal ion (e.g. alkali, alkaline earth or aluminium) in aconventional manner. This step is preferably conducted under operativeconditions which give essentially complete removal of residual fluoridespecies from the crystalline aluminophosphate. The preferred aqueoussolution for use in this step is an ammonium salt solution, such as a10% ammonium chloride or acetate solution.

When the aluminophosphates have been calcined such crystallinealuminophosphates can be rehydrated or washed with distilled water for asufficient time to remove entrapped metal halides, if any, from theframework of the aluminophosphate(s). Metal halides such as alkali metalhalides, alkaline earth metal halides and aluminum halides are removedfrom the crystalline aluminophosphate structure. Such metal halides canoccupy the pore volume surface and cause high water adsorption nearsaturation. Because many metal halides sublime at relatively lowtemperatures, the calcination treatment step at the indicated elevatedtemperatures can also be used to remove impurities from thealuminophosphate. In general, the washing time can vary from a fewminutes to several hours or longer. The total washing time will beinfluenced by the concentration and choice of crystallinealuminophosphate, the amount of metal halides blocking the porestructure of the aluminophosphate and other factors. The water washingstep of the present invention is preferably conducted to removeessentially all metal halides from the treated crystallinealuminophosphate.

In some instances it is desirable to have residual halogen-derivedcompounds present in an amount between about 0.05 and about 6 percent byweight halogen based on the total weight of the treated product andpreferably between about 0.1 and about 5 percent by weight halogen,since some catalytic reactions may benefit from the presence of halogenpresent as a result of treatment with such halogen-derived compounds.

The treated crystalline aluminophosphate (treated with halogen-derivedgas) can further undergo calcination at a temperature of from about 100°C. up to the crystal destructon temperature of the aluminophosphate.This calcination step may remove non-metallic cations such as ammoniumcations from the crystalline aluminophosphate. The calcination step, inaddition to the process step involving contacting the halogen-derivedgas with the aluminophosphate(s), provides for high purityaluminophosphate products.

The crystalline aluminophosphate compositions prepared in accordancewith the process of the present invention can be used as selectiveadsorbents or as catalysts in hydrocarbon conversion processes, forexample, catalytic cracking processes wherein said hydrocarbon iscontacted with a treated aluminophosphate at effective hydrocarbonconversion conditions. Representative hydrocarbon conversion processesinclude: cracking; hydrocracking; alkylation for both the aromatic andisoparaffin types; isomerization, including xylene isomerization;polymerization; reforming, hydrogenation, dehydrogenation;transalkylation; dealkylation; hydrodecyclization; hydrofining;dehydrocylization; and disproportionation processes. Further, thesecompositions may be employed to separate molecular species fromadmixture with molecular species having a less degree of polarity bycontacting said mixture with said treated aluminophosphates, preferablyactivated by heating at greater than 100° C., having at least one of themore polar molecular species whereby molecules of the more polarmolecular species are selectively adsorbed into intracrystalline poresystem thereof.

Although this invention has been described with respect to a number ofdetails, it is not intended that this invention should be limitedthereby. The examples which follow are intended solely to illustrate theembodiments of this invention which to date have been determined and arenot intended in any way to limit the scope and the intent of thisinvention.

EXPERIMENTAL PROCEDURE

In carrying out the process of this invention, it is advantageous toutilize a reactor having means for evacuating the gases therefrom aswell as means for regulating the temperature. The reactor used in theexamples for contacting the aluminophosphates with halogen-derived gasis an enclosed mild steel container resistant to corrosion byhalogen-derived gas. The reactor is approximately 17 inches in length by10 inches in width with a height of 4 inches and a total volume ofapproximately 11.8 liters. The reactor is equipped with a removable lidand a 1/4 inch stainless steel tubing inlet and outlet. The reactor isheated with a hot plate or an oven. The temperature of a sample in thereactor was measured with a thermocouple embedded in the sample. Thetemperature of the reactor is controlled to ±5° C. with a temperaturecontroller and the flow of halogen-derived gas and/or diluent wascontrolled with a series of rotometers. The aluminophosphates are placedinside the reactor in Teflon containers measuring approximately 4 inchesin length by 4 inches in width with a height of 1 inch. Thehalogen-derived gas is thoroughly mixed in a mixing chamber or cylinderbefore entering the reactor. Gas escaping from the reactor is directedto a scrubber system consisting of a soda lime trap vented to the top ofa hood. The general procedure includes: (1) introducing thealuminophosphate starting material into the reactor; (2) adjusting thetemperature to the indicated temperatures in the examples; (3) removingthe bulk of the air over the aluminophosphate sample by means of avacuum pump (a pressure of about 10⁻³ Torr is adequate) or flushing withnitrogen gas; (4) introducing the halogen-derived gas and/or diluentmixture at a minimal flow rate which results in a continuous flow of thegas mixture through the system for a period of time, e.g. about 1 minuteto about 10 hours; and (5) evacuating or flushing the reactor to removeresidual halogen-derived gas. Thereafter, the treated aluminophosphatemay be treated with an aqueous solution, i.e., ammonium salt solution,for a sufficient time to remove any aluminum fluoride cation species,i.e. AlF⁺⁺ and AlF₂ ⁺, from the treated aluminophosphate. The finalaluminophosphate product may then be stored in a sealed container toprevent reaction with water vapor.

The catalytic character of the aluminophosphates which have been treatedwith a halogen-derived gas were evaluated by test procedure involvingthe catalytic cracking of premixed n-butane at 2 mole percent in ahelium stream. The mixture containing 2 mole percent n-butane in heliumwas obtained from Union Carbide Corporation. The mixture underwentcracking in a one-half inch (outside diameter) quartz tube reactor intowhich was added 0.5 to 5.0 grams at 20-40 mesh of crystalline molecularsieve sample to be tested. The crystalline molecular sieve sample wasactivated in situ for 60 minutes at 500° C. under 200 cm³ /minute dryhelium purge. The mixture containing 2 mole percent n-butane in heliumis then passed at a rate of 50 cm³ /minute over the aluminophosphatesample for 40 minutes, with a product stream analysis carried out at 10minute intervals. The first order rate constant was then calculated todetermine the activity of the treated aluminophosphate as follows:

First Order Rate Constant (cm³ /gm min)=F 1n (1-c)/W wherein F is theflow rate in cm³ /min., W is the activated aluminophosphate sampleweight in grams and c is the mole fraction of n-butane consumed.

The following examples are provided to illustrated the invention and arenot intended to be limiting thereof:

EXAMPLE 1

AlPO₄ -5 was evaluated for its n-butane cracking constant and had avalue of 0.05. A five gram sample of AlPO₄ -5 was calcined at 600° C.for 2 hours in air. The calcined sample was then ion exchanged in a 10percent by weight solution of ammonium acetate in water under refluxconditions for 1 hour. The mixture was filtered and the solid washedwith 500 cubic centimeters of distilled water. The reflux and water washwere repeated two additional times and the material dried in air. Then-butane cracking constant was determined by the procedure abovedescribed, and was 0.05.

EXAMPLE 2

AlPO₄ -11 was evaluated to determine its n-butane cracking constant andwas determined to have a value of 0.05. AlPO₄ -11 was calcined andion-exchanged by a procedure similar to that employed in example 1 forAlPO₄ -5. The n-butane cracking constant of the ammonium exchanged AlPO₄-11 was 0.04.

EXAMPLE 3

Ten grams of AlPO₄ -5 as the calcined extrudate was treated with 2.5volume percent fluorine in a nitrogen stream (volume percent fluorinebased on the total volume of fluorine and nitrogen) for a period of 15minutes at a total flow rate of 1500 cubic centimeters per minute(cc/min) at room temperature (18° C. to 22° C.). A five gram portion ofthis sample was steamed for 2 hours and 45 minutes at a steamconcentration of 16 percent by weight and a temperature of 600° C. Thesteamed sample was analyzed by x-ray and observed to be highlycrystalline and of substantially the same crystallinity of the startingmaterial. The n-butane cracking constant of the steamed product was0.50.

EXAMPLE 4

A ten gram sample of AlPO₄ -5 was treated with 5 percent by volumefluorine in nitrogen (volume percent fluorine based on the total volumeof fluorine and nitrogen) for 30 minutes at a flow rate of 1500 cc/minat room temperature (18° C.-22° C.) and then purged for 10 minutes withnitrogen at a flow rate of 1500 cc/min. A portion of this sample wasammonium exchanged under reflux conditions and water washed as done inexample 1. The product was dried and the n-butane cracking constantdetermined to be 0.22.

We claim:
 1. A process for treating crystalline aluminophosphates whichcomprises contacting at an effective temperature for an effective timeto modify their adsorptive and/or catalytic properties said crystallinealuminophosphates a gas mixture comprising:(i) from 0.1 to 100 volumepercent of at least one gas selected from the group consisting offluorine, chlorine, bromine, iodine, and interhalogen compoundscontaining two or more halogens; (ii) from zero to 21 volume percenthalogen; and (iii) from 0 to 99.9 volume percent inert gas.
 2. Processaccording to claim 1 wherein at least one inert gas is present inaddition to (i) and (ii) in an amount from about 50 to 99.75 volumepercent.
 3. A process according to claim 1 further comprising ionexchanging the crystalline aluminophosphate product of claim 1 with anaqueous solution of at least one salt capable of removingaluminofluoride species from the crystalline aluminophosphate product.4. A process according to claim 3 wherein the aqueous solution is anaqueous ammonium salt solution.
 5. A process according to claim 1further comprising calcining the crystalline aluminophosphate product atan effective temperature of between about 100° C. and the crystaldestruction temperature of the aluminophosphate.
 6. A process accordingto claim 5 further comprising rehydrating the crystallinealuminophosphate after calcining the crystalline aluminophosphate.
 7. Aprocess according to claim 2 wherein the inert gas is selected from thegroup consisting of nitrogen, helium and mixtures thereof.
 8. A processof claim 1 wherein the effective temperature is between about 20° C. andabout 200° C.
 9. The process of claim 1 wherein said aluminophosphatehas a framework structure having a chemical composition expressed interms of mole ratios of oxides as:Al₂ O₃ : 1.0±0.2 P₂ O₅ each of saidframework structures being microporous in which the pores are uniformand have nominal diameters within the range of about 3 to about 10Angstroms, an intracrystalline adsorption capacity for water at 4.6 Torrand 24° C. of at least 3.5 weight percent, the adsorption and desorptionof water being completely reversible while retaining the same essentialframework topology in both the hydrated and dehydrated state.
 10. Theprocess of claim 9 wherein said aluminophosphate is selected from thegroup consisting of AlPO₄ -5, AlPO₄ -8, AlPO₄ -9, AlPO₄ -11, AlPO₄ -12,AlPO₄ -14, AlPO₄ -16, AlPO₄ -17, AlPO₄ -18, AlPO₄ -20, AlPO₄ -22, AlPO₄-25, AlPO₄ -26, AlPO₄ -28, AlPO₄ -31, and AlPO₄ -33.
 11. The process ofclaim 1 wherein the gas mixture comprises;(i) from about 0.25 to about50 volume percent of a halogen selected from the group consisting offluorine, chlorine, bromine, iodine and mixtures thereof; (ii) fromabout 0 to about 21 volume percent oxygen; and (iii) from about 50 toabout 99.9 volume percent of an inert gas.
 12. The process of claim 2wherein the gas mixture comprises from 1 to about 25 volume percentfluorine and an inert gas.
 13. A treated crystalline aluminophosphatecharacterized as having a framework structure having a chemicalcomposition expressed in terms of mole ratios of oxides as

    Al.sub.2 O.sub.3 : 1.0±0.2 P.sub.2 O.sub.5

each of said framework structures being microporous in which the poresare uniform and have nominal diameters within the range of about 3 toabout 10 Angstroms, an intracrystalline adsorption capacity for water at4.6 Torr and 24° C. of at least 3.5 weight percent, the adsorption anddesorption of water being completely reversible while retaining the sameessential framework topology in both the hydrated and dehydrated stateand having present between about 0.5 and about 6 percent by weighthalogen.
 14. The treated crystalline aluminophosphate of claim 13 havingbetween about 0.1 and about 5 percent by weight halogen.
 15. A processaccording to claim 3 wherein said aqueous solution contains ammonium,aluminum, alkali metal or alkaline earth metal.